code: def process_test_df():
      "Base DataFrame"
      return pd.DataFrame(
          {
              "text": ["a_b_c", "c_d_e", np.nan, "f_g_h"],
              "numbers": range(1, 5),
          }
      )
  
imports: import numpy
  import pandas
  import pytest
  from pandas.testing import assert_frame_equal
label_desc: Use image node_id 1 for calling a global function with example usage: process_test_df() and returns: pd